Stingrays inspire engineering research

“Most fish wag their tails to swim. A stingray's swimming is much more unique, like a flag in the wind.”

Richard Bottom, graduate student

Department of Mechanical and Aerospace Engineering

Recent studies show stingrays are the hybrid cars of the
ocean.

The flat fish move through water with such ease that researchers
from UB and Harvard University are studying how stingray movements
could be used to build more agile and maneuverable unmanned
underwater vehicles.

The vehicles could allow researchers to more efficiently study
the mostly unexplored ocean depths, as well as take part in cleanup
and rescue efforts.

“Most fish wag their tails to swim. A stingray’s
swimming is much more unique, like a flag in the wind,” says
Richard Bottom, a UB mechanical engineering graduate student who is
participating in the research. “I've always wondered why they
were unique. This research is figuring that out.”

Bottom and Iman Borazjani, assistant professor in the Department
of Mechanical and Aerospace Engineering, set out to investigate the
form-function relationship of the stingray: why does it look the
way it does and what does it achieve by moving the way it does?

Colleagues at Harvard, working with live stingrays, gathered
data on stingray body shape, motion, speed, etc. The UB researchers
took that data and used supercomputers and computational fluid
dynamics, a method of using algorithms to solve problems that
involve fluid flows, to calculate the flow of water and the
vortices around the live stingrays.

Borazjani and Bottom will explain the relationship and their
findings on Nov. 24 at the 66th Annual Meeting of the American
Physical Society Division of Fluid Dynamics in Pittsburgh. Their
lecture is titled “Biofluids: Locomotion III —
Flying.”

Borazjani’s previous work, which was published in
Proceedings of the Royal Society, examined the leading-edge vortex
— the vortex at the front edge of the object in motion
— for the first time in underwater locomotion. The
leading-edge vortex has been observed in the flight of birds and
insects, and is one of the most important thrust-enhancement
mechanisms in insect flight, Borazjani explains.

The same vortex is found in swimming stingray. The vortices on
the waves of the stingrays’ bodies cause favorable pressure
fields — low pressure on the front and high pressure on the
back — that push the ray forward. Because movement through
air and water are similar, understanding vortices is critical.

“By looking at nature, we can learn from it and come up
with new designs for cars, planes and submarines,” says
Borazjani. “But we’re not just mimicking nature. We
want to understand the underlying physics for future use in
engineering or bio-inspired designs.”

Studies already have shown that stingray motion closely
resembles the most optimal swimming gait, says Bottom. Much of this
is due to the stingray’s unique flat and round shape, which
allows it to easily glide through water.

But while the stingray’s distinctiveness has earned it
attention in the lab, it plays a comforting role in Bottom’s
life as well. In addition to attending graduate school, Bottom
works full time as an applications engineer at Niagara Thermal
Products, where he handles new product development.

“Whenever schoolwork gets to be too much, I park myself in
front of my fish tank and relax,” says Bottom, who owns a pet
ray. “There is something mesmerizing about watching a
stingray.”

The research placed first in the UB Mechanical Aerospace
Engineering Graduate Poster Competition. Borazjani and Bottom plan
to continue their research and study the differences in movement
among several types of rays.